Progressive Supranuclear Palsy (PSP) and Alzheimer's disease (AD) are neurodegenerative diseases which afflict mostly older individuals. The neuropathologic hallmark of both of these disorders is an accumulation of neurofibrillary tangles within neurons in different regions of the brain. The specific aims of this project are to define specific post-translations modifications occurring on tau proteins which are involved in the formation of neurofibrillary tangle pathology in PSP and to isolate and characterize the molecules that initiate and/or perpetuate this process. The tangle pathology will be immunochemically characterized with well- defined antibodies directed against specific tau1 paired helical filament (PHF) and ubiquitin epitopes. These results will be correlated with its ultrastructural morphology and neuroanatomic distribution. Molecular biological approaches utilizing a novel yeast two-hybrid system and/or lambda phage expression libraries will be used to isolate and identify potential protein gene products that interact with tau proteins. The cDNA clones will be characterized by RNA hybridization methods, including Northern blot analysis, RNase protection assay, and in situ hybridization, in order to study their expression distribution in normal and diseased human brain tissue. The putative interaction with tau proteins will be examined by transfection of cultured cell lines expressing either endogenous or exogenous tau proteins. Recombinant protein gene product will be produced in a bacterial expression system and will be used to generate specific antibodies. Successful identification of tau-interacting protein molecules will increase our understanding of normal tau protein function and may reveal how abnormally modified tau proteins are involved in neurofibrillary tangle pathology. This project focuses on PSP because of its relatively pure tangle pathology, but the results will very likely be applicable to studies of neurodegeneration of aging brain and Alzheimer's disease.